1. Field of the Invention
The present invention relates to a photoelectric smoke detector whose light receiving section receives light which is originated from a light-emitted section and is scattered by smoke flowing into a smoke detection section, thereby detecting occurrence of fire, as well as to a smoke detection section assembly. More particularly, the present invention relates to a photoelectric smoke detector using a hybrid circuit board, which board has mounted thereon an integrated circuit component including a light-receiving element and an amplifier circuit, in conjunction with other circuit components, as well as to a smoke detection section assembly.
2. Description of the Related Art
FIGS. 24 through 27 show a commonly-employed photoelectric smoke detector, wherein FIG. 24 is a longitudinal cross-sectional view of the smoke detector; FIG. 25 is a transverse cross-sectional view of the smoke detector; FIG. 26 is a layout and construction drawing of a smoke detecting section; and FIG. 27 is a disassembly view of the smoke detector.
As shown in FIGS. 24 and 25, a terminal board 203 is housed in an exterior cover 201, and a shield case 204 is fixedly attached to the interior of the terminal board 203. A smoke detection section main unit 205 is fitted to the terminal board 203, and a printed board 208 is provided on the smoke detection section main unit 205. A plurality of smoke inlets 202 are formed along the circumference of the exterior cover 201.
A smoke detection section cover 211 is removably attached to the lower surface of the smoke detection section main unit 205. Smoke inlets 215 are formed in the circumferential wall of the smoke detection section cover 211. A plurality of labyrinthine members 213 are formed inside the circumferential wall. An insect screen 214 is provided integrally on the smoke-detecting section 211.
A light-emission element 221, such as an infrared LED or the like, is housed in a light-emission holder 217 provided on the lower surface of the smoke detection section main unit 205. A light-receiving holder 216 houses a light-receiving element 220, such as a photodiode PD or the like. As can be seen from FIG. 26, the optical axis of the light-emission element 221 and the optical axis of the light-receiving element 220 are arranged so as to cross each other in the center of a smoke detecting space and at an angle of, for example, 70.degree.. Here, reference numeral 228 designates an infrared LED for test purpose, and 232 designates a plate member having a slit formed therein.
As shown in FIG. 27, the above-described smoke detector is built by means of assembling together the terminal board 203 having fitting metal fitting 209 fixed thereon; the shield case 204; packing 207, the printed board 208; the smoke detection section main unit 205; the smoke detection section cover 211; and the exterior cover 201.
In such a commonly employed photoelectric smoke detector, the light-receiving element 220 is housed in the light-receiving holder 216 and is connected to the printed board 208 disposed on the smoke detection section main unit 205 by means of lead wires. When flowing through lead wires, a faint light-receiving signal is prone to external noise. In order to protect the light-receiving signal from external noise, a metal shield cap 227 is provided within the light-receiving holder 216.
Electric circuit components to be mounted on the printed board 208 are made compact by means of being made in the form of chip components. Further, the number of components is reduced by means of optimization of circuit design. However, there are limitations to further miniaturization of an electric circuit and to a further reduction in the number of electric circuit components.